UN inspectors say they have "clear and convincing evidence" that chemical weapons were used "on a relatively large scale" against civilians, including children, in an August attack in Syria.

UN Secretary-General Ban Ki-moon presented the long-awaited reportto a closed-doormeeting of the UN Security Council on September 16.

The report, drafted by UN inspectors led by Swedish chemical-weapons expert Ake Sellstrom, says "environmental, chemical and medical" evidence they gathered in Syria suggests that surface-to-surface rockets containing the nerve agent sarin were used in the Gouta area of Damascus on August 21.

Ban told the Security Council that UN inspectors have confirmed, "unequivocally and objectively," that chemical weapons have been used in Syria. He called it a "war crime" and said the perpetrators must be brought to justice.

"The mission has provided the world with an impartial and independent account," he said. "The results are overwhelming and indisputable. Eighty-five percent of the blood samples tested positive for sarin."

The UN inspectors were not empowered to investigate who was responsible for the chemical attacks -- the regime of Syrian President Bashar al-Assad or opposition rebels.

But Britain, France, and the United States all said the UN report left "no doubt" that Assad's regime was responsible for the poison-gas attack.

White House spokesman Jay Carney said only the Assad regime has access to the surface-to-surface rockets used in the attacks. The information provided in the UN report, he said, "makes clear the responsibility."

French Foreign Minister Laurent Fabius, speaking in a radio interview, said "the quantities of the toxic gas used, the complexity of the mixes, the nature and the trajectory of the [gas] carriers...leave absolutely no doubt as to the origin of the attack. It reinforces the position of those that have said the regime is guilty."

Russia's ambassador to the UN, Vitaly Churkin, said the inspectors' report contained no clear indications as to who was responsible for the August 21 attack.

The United States has consistently blamed Assad's regime for the attack, which Washington says killed some 1,400 people, including 400 children.

The Syrian government denies it used chemical weapons. Syria and Russia have blamed the Gouta attack on rebels.

The release of the UN inspectors' report came two days after Russia and the United States agreed to a plan to destroy Syria's chemical weapons within a year.

The agreement averted the threat of imminent U.S. military strikes in Syria.

U.S. President Barack Obama said on September 16 that the U.S.-Russia agreement was an "important step" toward ending the threat of Syria's chemical arsenal.

But he cautioned that it must be properly implemented, adding, "we are not there yet."

The UN report came hours after the foreign ministers of France, Britain, and the United States agreed at talks in Paris to seek a "strong and robust" UN resolution that sets precise and binding deadlines on the removal of chemical weapons.

U.S. Secretary of State John Kerry, speaking after the talks, said the Damascus regime would "play games" if the UN resolution is seen as weak or unenforceable.

He added that Russia had agreed there would be "consequences" if Assad failed to implement the agreement.

"We know that even the UN inspectors who were there recently had difficulties getting access in some places," Kerry said. "That is why in Geneva the Russians agreed with us that there should be unfettered, unrestricted access to sites [of chemical weapons] in order to make certain we do this as rapidly as is possible."

Kerry said the agreement on Syria that he reached in Geneva on September 14 with Russian Foreign Minister Sergei Lavrov indicates Moscow is ready to support a UN Security Council resolution under Chapter 7 of the UN Charter.

Chapter 7 outlines possible UN authorization of sanctions and military action in response to "threats to the peace" and "acts of aggression."

But Lavrov, speaking September 16 in Moscow, said any UN resolution would not mention the threat of force.

"Our American colleagues very much wanted to have a resolution adopted on the basis of Chapter 7," Lavrov said. But the final agreement adopted in Geneva, he added, "contains no such reference."

The chairman of a UN war crimes panel in Geneva said it is investigating 14 suspected chemical attacks in Syria. Paulo Sergi Pinheiro said September 16 the panel had not pinpointed the chemical used or who was responsible.